Cell death occurs in the medial-edge epithelium (MEE) of the secondary palatal shelf at the time of epithelial fusion. Moreover, just prior to fusion a transient increase in cyclic adenosine 3':5' monophosphate (cAMP) occurs and cytochemical localization of adenylate cyclase is restricted to degenerating MEE cells. Proposed research will focus on the regulatory role of cyclic nucleotides in palatal MEE cell degeneration in an attempt to elucidate specific biochemical aspects underlying the mechanisms of normal and abnormal palatal development. Developing palatal shelves and eyelids in the chick embryo provide tissues in which epithelial fusion normally fails to occur, purportedly due to the absence of epithelial cell death. In contrast, cell death is known to be a normal component of development of the limbs, primary and secondary palate and rodent placental giant cells. Radioimmunoassay for levels of cAMP and cyclic guanosine 3':5'-monophosphate (cGMP) in these tissues should provide insights into the contributions of cyclic nucleotides to normal cellular degeneration. Localization of endogenous cAMP and cGMP utilizing indirect immunofluorescence is proposed in these tissues to permit detection of those populations of cells responsible for biochemically determined alterations in endogenous cyclic nucleotide levels. Since a beta-type norepinephrine-sensitive adenylate cyclase is known to be present in the developing rodent palate, dry autoradiography and fluorescent beta-adrenergic blocking agents will be used to localize beta-adrenergic receptors and define those "factors" responsible for activating epithelial adenylate cyclase with subsequent elevation of intracellular cAMP. Beta-adrenergic receptors in the palate will be quantitated by binding assays. By comparing these quantitative data with those obtained in the localization studies, it will be possible to (1) correlate cytochemical localization of ligand binding with quantitation of receptor levels during palatal development and (2) examine the relationship between the number of beta adrenergic receptors and the behavior of adenylate cyclase in the developing secondary palate.